1. Field of the Invention
The present invention relates to a packaging carton, in particular to a packaging carton having a which has flange, on the upper face of which a sealing cover such as a transparent film can be bonded by fusion or adhesion with adhesives, so that it can be manufactured inexpensively and efficiently.
2. Description of the Related Art
Packaging cartons are traditionally manufactured by forming a sheet of film material, synthetic paper, or resin material with a forming tool. This manufacturing method requires an expensive forming tool which, when various kinds of packing cartons are manufactured, must be individually provided for each kind of the packing carton requiring much time and a large financial burden. In order to avoid this disadvantage, there is a method by which a packaging carton is provided by cutting a quadrilateral sheet from a strip sheet of film or paper conveyed in the longitudinal direction; providing the quadrilateral sheet with a first, second and third outward folding lines, a first, second and third inward folding lines, and angled inward folding lines; and folding the quadrilateral sheet to form a tray having a stepped flange around the periphery of the tray (JP-A-6-72425).
Moreover, there is a packaging technique in which a tray carton having a flange around the periphery thereof, is folded up from a carton blank cut in a specified shape (JP-A-60-240444 and U.S. Pat. No. 4,636,187, both being foreign applications of U.K. Patent 2158392).
However, the packaging cartons disclosed in the above patent documents have following drawbacks. In the former, the carton is formed with a flange being stepped without being formed to be flat making it difficult to bond a sealing cover, such as a transparent film, by fusion or adhesion with adhesives. In the latter, the periphery of the carton blank must be cut in a specified shape for the folded up tray to provide a flange around the periphery thereof, which may cause chips of the carton blank to enter inside the tray carton. This makes the tray carton unsuitable as a packaging carton for packing foods.
The present invention was made in order to eliminate the above drawbacks with an object of providing a packaging carton which has a flat formed flange on the upper face of which a sealing cover such as a transparent film can be bonded, and can be inexpensively manufactured with high efficiency.